Women who are pregnant or trying to get pregnant may need to forgo coffee, tea, sodas and other sources of caffeine. A new data analysis finds no safe level of the drug during this time.
"The cumulative scientific evidence supports pregnant women and women contemplating pregnancy being advised to avoid caffeine," concluded study author Jack James, a professor at Reykjavik University in Iceland.
The findings challenge current U.S. expert recommendations from organizations such as the March of Dimes and the American College of Obstetricians and Gynecologists. Those guidelines say that consuming a small amount of caffeine each day -- 200 milligrams, equal to about a cup or two of coffee -- does not appear to harm the fetus.
In the new analysis, James tracked data from 37 studies and 11 meta-analyses (data gleaned from multiple studies) published over the past two decades. The study focused on six major negative pregnancy outcomes: miscarriage, stillbirth, low birth weight and/or babies small for gestational age, preterm birth, childhood acute leukemia, and childhood overweight/obesity.
Of the 42 separate findings in the observational studies, 32 found that caffeine significantly increased the risk of a negative pregnancy outcome, while 10 others found either no associations or inconclusive associations. Caffeine-related risks were reported with moderate to high levels of consistency for all pregnancy outcomes except preterm birth.
Of the 17 findings from the meta-analyses, 14 concluded that caffeine was associated with an increased risk for four adverse pregnancy outcomes: miscarriage, stillbirth, low birth weight and/or small for gestational age, and childhood acute leukemia.
The other three meta-analyses didn't find an association between caffeine consumption and increased risk of preterm birth.
None of the meta-analyses examined the association between maternal caffeine consumption and childhood overweight and obesity, but four of five observational studies reported significant associations, according to the report published online Aug. 24 in the journal BMJ Evidence-Based Medicine.
James stressed that all of the data in the analysis came from observational studies, which aren't designed to establish cause and effect.
However, his findings show there is "substantial cumulative evidence" of an association between caffeine consumption and a number of negative pregnancy outcomes, he said in a journal news release. Those negative outcomes include miscarriage, stillbirth, low birth weight and/or small for gestational age, childhood acute leukemia and childhood overweight and obesity, but not preterm birth.
That suggests that current health recommendations about caffeine consumption during pregnancy are in need of "radical revision," according to James.
Dr. Jennifer Wu is an obstetrician/gynecologist at Lenox Hill Hospital in New York City. Reading over the new findings, she said that "in the last 20 years, small studies have indicated that the recommendation for caffeine in pregnancy should be decreased to smaller doses."
She agreed with James that, based on his work, "the counseling for patients considering pregnancy needs to change."
Wu said, "This meta-analysis brings together many studies and the power of the larger numbers indicates that caffeine may need to be avoided altogether in pregnancy. There are serious significant risks that hold true across many studies."
The U.S. Food and Drug Administration has more on caffeine.